The present embodiments relate to a technique which measures the rate of solidification of crystalline/amorphous inks. The crystalline/amorphous inks are phase change ink compositions characterized by being solid at room temperature (e.g., 20-27° C.) and molten at an elevated temperature at which the molten ink is applied to a substrate. These phase change ink compositions can be used for ink jet printing. The present embodiments are directed to a novel application of a known TROM technique to identify a novel way of testing new ink compositions to make sure they are fast solidifying, which is illustrated by a rapidly solidifying phase change ink composition.
A key requirement for inks in the production environment is high speed printing in a Direct to Paper (DTP) architecture. Suitable inks are made of an ink base that is comprised of amorphous and crystalline components with additives like colorants. Fast printing requires the ink to solidify quickly, which translates into a requirement for fast crystallization. In order to design fast crystallization, ink jet printing processes may employ inks that are solid at room temperature and liquid at elevated temperatures. Such inks may be referred to as solid inks, hot melt inks, phase change inks and the like. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing phase change ink for printing on a recording medium such as paper. In piezo ink jet printing processes employing hot melt inks, the phase change ink is melted by a heater in the printing apparatus and utilized (jetted) as a liquid in a manner similar to that of conventional piezo ink jet printing. Upon contact with the printing recording medium, the molten ink solidifies rapidly, enabling the colorant to substantially remain on the surface of the recording medium instead of being carried into the recording medium (for example, paper) by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a phase change ink in ink jet printing are thus elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
In general, phase change inks (sometimes referred to as “hot melt inks”) are in solid phase at ambient temperatures, but exist in liquid phase at elevated operating temperature of an ink jet printing device. At the jetting temperature, droplets of liquid ink are ejected from the printing device, and when liquid droplets contact the surface of the recording medium, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops.
Phase change inks for color printing typically comprise a phase change ink carrier composition which is combined with a phase change ink compatible colorant. In a specific embodiment, a series of colored phase change inks can be formed by combining ink carrier compositions with compatible subtractive primary colorants. The subtractive primary colored phase change inks can comprise four component dyes or pigments, namely, cyan, magenta, yellow and black, although the inks are not limited to these four colors. These subtractive primary colored inks can be formed by using a single dye or pigment or a mixture of dyes or pigments. For example, magenta can be obtained by using a mixture of Solvent Red Dyes or a composite black can be obtained by mixing several dyes. U.S. Pat. No. 4,889,560, U.S. Pat. No. 4,889,761, and U.S. Pat. No. 5,372,852, the disclosures of each of which are totally incorporated herein by reference, teach that the subtractive primary colorants employed can comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and Basic Dyes. The colorants can also include pigments, as disclosed in, for example, U.S. Pat. No. 5,221,335, the disclosure of which is totally incorporated herein by reference. U.S. Pat. No. 5,621,022, the disclosure of which is totally incorporated herein by reference, discloses the use of a specific class of polymeric dyes in phase change ink compositions.
Phase change inks are desirable for ink jet printers because they remain in a solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording medium (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the recording medium, so that migration of ink along the printing medium is prevented and dot quality is improved.
While the above conventional phase change ink technology is successful in producing vivid images and providing economy of jet use and substrate latitude on porous papers, such technology has not been satisfactory for coated substrates. Thus, while known compositions and processes are suitable for their intended purposes, a need remains for additional means for forming images or printing on coated paper substrates. As such, there is a need to find alternative compositions for phase change ink compositions and future printing technologies to provide customers with excellent image quality on all substrates, including selecting and identifying different classes of materials that are suitable for use as desirable ink components. There is a further need for printing these inks at high speeds as required by digital presses in production environment.
Fast printing requires that the inks solidify quickly and this translates into a requirement for fast crystallization. In order to develop fast crystallizing inks, it is necessary to develop efficient methods to measure the rate of crystallization.
Currently, there are two available method for determining suitability of an ink for high speed printing. The first is to actually print the test ink with the intended printer, at the desired speed and test whether there is any visible ink transferred on the next page. If this is the case, the ink solidified too slowly and is not suitable. A fast crystallizing ink would not offset on the next page when printed at the desired speed. This approach requires using of significant amounts of inks for testing and therefore it is expensive and time consuming. There is a need to develop a method to characterize the rate of crystallization of crystalline-amorphous ink which uses very small amounts of materials (i.e., less than 1 gram) and which could be performed in short time in order to enable fast and cost effective screening of inks. The second method consists of K-proofing the inks. This method has several disadvantages. One disadvantage is that there is at least a few seconds delay between producing the K-proof and then testing the solidification of the ink on the print. Thus, the method does not offer information to distinguish between the desirable links which crystallize within 5 seconds of printing.
Polarized Optical Microscopy (“POM”) was previously utilized to view crystallization of crystalline polymers. For example, in Andjelic' S, Jamiolkowski D D, McDivitt J, Fischer J, Zhou J. J Polym Sci, Polym Phys Ed 2001; 39:3073, optical microscopy was performed with a Nikon SHZ-U optical microscope in conjunction with a Micron i308 low light integrating camera and all observations were viewed through crossed polarizations. The polymer sample was held in the Linkam shear stage, providing precise temperature and shear control. All images were captured at a 6 times magnification, and a scale bar is shown in the microscopy figures. For enhancement in appearance for publication, all optical microscopy images have been contrast-inverted; dark fields are light and vice versa. In addition, in an article entitled “Crystallization Behavior of Poly(ethylene oxide) in the Presence of Na+ Montmorillonite Fillers,” by K. E. Strawhecker and E. Manias, Jan. 25, 2003 (American Chemical Society., the authors utilized an Olympus BH-2 Optical Microscope, equipped with a Mettler hot stage (RT-300° C.) and a video camera connected to a VCR. The crystallization behaviour of all systems was recorded in real-time video to be utilized in later analysis of crystallization shapes and formation. In these examples, crystalline or semi-crystalline polymer samples were held on the heating/cooling stage at all times in order to achieve very high temperature control. In addition, samples were cooled at low rate such as 0.25 to 10° C. per minute.
Accordingly, there is a need for a method which enables quick screening of a test ink batches without the need to scale-up ink formulations to 100 s of grams or kilograms of ink. Each of the foregoing U.S. patents and patent publications are incorporated by reference herein. Further, the appropriate components and process aspects of the each of the foregoing U.S. patents and patent publications may be selected for the present disclosure in embodiments thereof.